EEG (brainwave) signals have been extensively studied in an effort to determine relationships between frequencies of electrical activity or neural discharge patterns of the brain and corresponding mental, emotional or cognitive states. Biofeedback of identified frequency bands of EEG signals is used to enable a person to voluntarily reach or maintain a target mental state.
Frequency bands of EEG readings used in such biofeedback have been generally categorized in the approximate frequency ranges of:
delta waves, 0 to 4 Hz;
theta waves, 4 to 7 Hz;
alpha waves, 8 to 12 Hz;
beta waves, 12 Hz to 36 Hz, and
sensorimotor rhythm (SMR) waves, 12 to 15 Hz.
It is theorized that each of the major subbands of biofeedback EEG (delta, theta, alpha, beta) has unique bio-electric characteristics which correspond with unique subjective characteristics of an individual. The delta band is observed most clearly in coma and deep sleep, the theta band in light sleep and drowsiness, the alpha band in a variety of wakeful states involving creativity, calm and inner awareness, and the beta band in alert wakeful situations with external focus. In general, a dominant brain wave frequency increases with increasing mental activity.
Many different approaches have been taken to EEG biofeedback to achieve mental state control. U.S. Pat. No. 4,928,704 describes a biofeedback method and system for training a person to develop useful degrees of voluntary control of EEG activity. EEG sensors are attached to cortical sites on the head for sensing EEG signals in a controlled environmental chamber. The signals are amplified and filtered in accordance with strict criteria for processing within time constraints matching natural neurologic activity. The signals are filtered in the pre-defined subbands of alpha, theta, beta and delta, and fed back to the monitored person in the form of optical, aural or tactile stimuli.
U.S. Pat. No. 4,949,726 discloses an electrical device which is responsive to recorded brain waves to produce an electrical output which corresponds to detection of brain waves in predefined frequency ranges. The output of the device is connected to a device control apparatus to cause an output device to perform a function in accordance with detected brainwave signals. U.S. Pat. No. 5,024,235 describes an EEG neurofeedback apparatus which detects analog signals from the brain, converts readings to digital signals and compares the digital signals to a threshold amplitude to provide an auditory or visual indication to a person of whether or not the detected signals are within a predetermined frequency range.
U.S. Pat. No. 5,241,967 describes a system for evoking EEG signals from a subject which applies a frequency signal to a stimulus generator for conversion to a stimulative signal such as a photic stimulus to the subject. The brain wave to be evoked is strongly synchronized by the stimulative signal applied to the subject to put the subject in the desired brain wave state. U.S. Pat. No. 5,365,939 describes a method for evaluating and treating an individual with EEG disentrainment feedback by selecting a reference site to determine a reference brain wave frequency, entraining the brain wave frequency in one direction until a first stop condition occurs, the entraining the brain wave frequency in an opposite direction until a second stop condition occurs. Different electrode sites are selected to fully test an individual for flexibility to EEG entrainment feedback treatment. And U.S. Pat. No. 5,406,957 describes an EEG Neurofeedback apparatus for training and tracking of cognitive states which measures bioelectric signals in bandwidth windows to produce a composite amplitude by a fast Fourier transform on an amplified signal. Selected bandwidths are displayed and monitored by computer to enable training of a person being monitored with audio or verbal feedback.
In many of the EEG biofeedback systems and methods of the prior art, it is necessary to interrupt data collection and analysis and/or the biofeedback process in order to perform set-up functions, to review component values, or to set protocols or adjust threshold levels. These functions are typically performed by a session administrator, which can ultimately diminish or otherwise adversely effect the nature and quality of biofeedback signals to a subject seeking to benefit from EEG training.
Most of the neurofeedback systems of the prior art generate only a single form of each type of feedback stimuli, such as a single screen display, or a single auditory and tactile signal, thus inherently limiting the scope of biofeedback and physical (EEG) response.